On Wed, 2017-04-12 at 09:36 +0800, gfree.w...@foxmail.com wrote:
> From: Gao Feng <f...@ikuai8.com>
>
> 1. Don't get the metric RTAX_ADVMSS of dst.
> There are two reasons.
> 1) Its caller dst_metric_advmss has already invoke dst_metric_advmss
> before invoke default_advmss.
> 2) The ipv4_default_advmss is used to get the default mss, it should
> not try to get the metric like ip6_default_advmss.
>
> 2. Use sizeof(tcphdr)+sizeof(iphdr) instead of literal 40.
>
> 3. Define one new macro IPV4_MAX_PMTU instead of 65535 according to
> RFC 2675, section 5.1.
trivia:
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
[]
> @@ -1250,14 +1250,11 @@ static void set_class_tag(struct rtable *rt, u32 tag)
>
> static unsigned int ipv4_default_advmss(const struct dst_entry *dst)
> {
> - unsigned int advmss = dst_metric_raw(dst, RTAX_ADVMSS);
> + unsigned int header_size = sizeof(struct tcphdr) + sizeof(struct iphdr);
> + unsigned int advmss = max_t(unsigned int, dst->dev->mtu - header_size,
> + ip_rt_min_advmss);
>
> - if (advmss == 0) {
> - advmss = max_t(unsigned int, dst->dev->mtu - 40,
> - ip_rt_min_advmss);
> - if (advmss > 65535 - 40)
> - advmss = 65535 - 40;
> - }
> + advmss = min_t(unsigned int, advmss, IPV4_MAX_PMTU - header_size);
as all the elements are now unsigned int, the min_t cast
seems unnecessary.
